I saw humpback whales save a seal from death by killer whale

When Robert Pitman realised he had just witnessed an organised rescue mission by humpback whales, he had to find out why

Robert Pitman, marine ecologist

Robert Pitman

By Joshua Howgego

You first saw humpback whales behaving strangely in 2009. What happened?

We were doing killer whale research in Antarctica and had the BBC on board filming Frozen Planet. We saw some killer whales interacting with some humpbacks and thought it could be an attack. We went over to have a look and the humpbacks were a little agitated, but it wasn’t a full-on attack and the killer whales ended up going away. We weren’t quite sure what was going on, but when we looked at the BBC footage, we saw there was a Weddell seal between the two humpbacks. So we thought maybe the seal was trying to escape and found refuge.

We followed the killer whales and soon they started attacking a crabeater seal on an ice floe, creating waves to try to wash it off. A few minutes later, the two humpbacks we had left behind came charging in and chased after the killer whales, slapping their flippers and making a nuisance of themselves. This was different because the humpbacks were on the offensive. But we figured it was just mobbing behaviour, like when garden birds mob a predator to try to get rid of it.

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When did you realise the whales were doing more than just driving a predator away?

Well, a couple of days later we saw some killer whales attacking a Weddell seal on an ice floe and there were a couple of humpbacks in the vicinity. We could tell they were agitated because we could hear them bellowing – it’s an impressive sound. The killer whales washed the seal off the ice and it started swimming into open water. Then, suddenly, one of the humpbacks comes to meet the seal and, just as it gets to the seal, rolls over on its back and the water washes the seal onto its chest. The whale lifts its chest up out of the water with the seal on it.

That sounds like pretty unusual behaviour for a whale…

Yeah – we were amazed to see it. But we immediately thought maybe the whale didn’t know the seal was there, maybe this was all just coincidence. Then we looked at the BBC footage, and we saw that at one point the seal had started to slip off the whale’s chest. The humpback used a 5-metre-long, 1-tonne flipper to gently nudge the seal back up onto its chest. Once we saw that, we knew it was no accident and something was going on.

What did you think was happening between the humpbacks and the seal?

It looked like altruism – as if the whales were acting out of concern for the smaller animal. But we are not talking about humans here, and when animals do something that appears to be altruism, I try to come up with rational explanations for it. But the reason wasn’t obvious because, as best we know, animals always act in their own self-interest. “This needs an explanation,” I thought.

What about other cetaceans — does their behaviour offer clues as to what was going on?

So you set out to look for evidence of humpbacks disturbing killer whale hunts…

When we got back from the trip, I wrote to everyone I knew working on killer whales and humpbacks. I got several dozen responses from people saying they had seen something similar. I also checked the literature and found other examples. A lot of these were from naturalists or even tourists on whale-watching boats, but that makes sense as there are a lot more of them watching whales than biologists doing so. This showed me that there are records of this behaviour wherever there are humpbacks.

Are other researchers persuaded that humpbacks are helping other species?

It has taken a while to convince people. In the animal world, altruism is a thorny issue because it can be difficult to explain in terms of natural selection. While certain acts can look like they are driven by compassion, researchers are wary of attributing such feelings to animals. It’s amazing how it raises hackles. But people got to know I was doing this research and they started looking at these interactions a little differently. Over the years, the number of sightings has built up to a critical mass. I think a lot of people who watch humpbacks now essentially agree with my interpretation of what is going on – although maybe not about why the humpbacks are doing it.

“Suddenly, the humpback rolls over and washes the seal safely onto its chest“

So are the whales being altruistic?

If you define altruism as a behaviour that increases the recipient’s fitness at the cost of the performer’s, then it’s pretty clear that this is altruism. Humpbacks are coming in to drive off killer whales. That seems to be humpbacks acting against their own best interests.

Killer whales are fearsome animals. Why would humpbacks get involved?

Humpbacks spend their lives going to the feeding and breeding grounds their mother took them to, so they are more likely to be related to nearby individuals than to the population as a whole. As a result, it’s in their interest to drive off killer whales that are attacking a nearby calf because they might be related. And humpbacks are so big and powerful, they have nothing to fear from killer whales – it’s only the calves that are vulnerable. The killer whales respect them: if a humpback were to slap its tail on a killer whale, it could kill it outright.

It also turns out that humpbacks charge in when killer whales begin vocalising. There are reports of humpbacks coming in from 2 kilometres away. They don’t know what the killer whales are attacking. It seems like the humpbacks have one simple instinct: when killer whales attack, you go in and try to stop them. So we think what’s going on here is inadvertent altruism.

Is it altruism if it is inadvertent?

It is according to the definition I gave earlier. The key point is that the behaviour shows how altruism could evolve out of self-interest. Indeed, in animals it is really just another form of self-interest. I wouldn’t be surprised if ultimately it is for humans too, because we admire altruism and it has its rewards: if you’re a war hero, you get ticker-tape parades. Admittedly, human altruism is more complicated than that. With animals, I think it’s relatively straightforward. Altruism has a place in their behaviour if it can be shown to be motivated by self-interest, and I think that is what’s going on with humpbacks. You don’t use terms like compassion and morality to explain this – it makes Darwinian sense.

Is there more to learn about whale behaviour?

Twentieth-century whaling reduced populations to the point where oceans were almost devoid of whales. But we’ve noticed a definite increase in numbers and I think their populations are beginning to recover to the point where we are seeing behaviours that we had no idea were out there. We need to be prepared for some more surprises in the way these animals interact with each other.

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Robert Pitman is a marine ecologist with the National Oceanic and Atmospheric Administration in La Jolla, California. His paper on humpback whale behaviour appears in Marine Mammal Science (DOI: 10.1111/mms.12343)